Isolation structure and device structure including the same

Abstract

An isolation structure is described, including a doped semiconductor layer disposed in a trench in a semiconductor substrate and having the same conductivity type as the substrate, gate dielectric between the doped semiconductor layer and the substrate, and a diffusion region in the substrate formed by dopant diffusion through the gate dielectric from the doped semiconductor layer. A device structure is also described, including the isolation structure and a vertical transistor in the substrate beside the isolation structure. The vertical transistor includes a first S/D region beside the diffusion region and a second S/D region over the first S/D region both having a conductivity type different from that of the doped semiconductor layer.

1. An isolation structure, comprising:
 a doped semiconductor layer in a trench in a semiconductor substrate, having the same conductivity type as the substrate; 
 gate dielectric between the doped semiconductor layer and the substrate; and 
 a diffusion region disposed besides a source/drain (S/D) region in the substrate, formed by dopant diffusion through the gate dielectric from the doped semiconductor layer, wherein the diffusion region has a first conductivity type and the source/drain region has a second conductivity type. 
 
     
     
       2. The isolation structure of  claim 1 , wherein the first conductivity type is p-type and the second conductivity type is n-type. 
     
     
       3. The isolation structure of  claim 1 , wherein the first conductivity type is n-type and the second conductivity type is p-type. 
     
     
       4. The isolation structure of  claim 1 , wherein the doped semiconductor layer comprises doped poly-Si. 
     
     
       5. The isolation structure of  claim 1 , further comprising a metallic layer in the trench and under the doped semiconductor layer, wherein the gate dielectric is also between the metallic layer and the substrate. 
     
     
       6. The isolation structure of  claim 5 , wherein the metallic layer comprises titanium nitride (TiN) or tantalum nitride (TaN). 
     
     
       7. A device structure, comprising:
 a semiconductor substrate having a first conductivity type; 
 an isolation structure, including a first doped semiconductor layer having the first conductivity type in a first trench in the substrate, gate dielectric between the first doped semiconductor layer and the substrate, and a diffusion region in the substrate formed by dopant diffusion through the gate dielectric from the first doped semiconductor layer; 
 a first vertical transistor in the substrate at a first side of the isolation structure, including a first source/drain (S/D) region beside the diffusion region and a second source/drain (S/D) region over the first S/D region both having a second conductivity type. 
 
     
     
       8. The device structure of  claim 7 , wherein the isolation structure further includes a metallic layer in the first trench and under the first doped semiconductor layer, and the gate dielectric is also between the metallic layer and the substrate. 
     
     
       9. The device structure of  claim 8 , wherein the metallic layer comprises titanium nitride (TiN) or tantalum nitride (TaN). 
     
     
       10. The device structure of  claim 7 , wherein the first conductivity type is p-type and the second conductivity type is n-type. 
     
     
       11. The device structure of  claim 7 , wherein the first conductivity type is n-type and the second conductivity type is p-type. 
     
     
       12. The device structure of  claim 7 , wherein the first doped semiconductor layer in the isolation structure comprises doped poly-Si. 
     
     
       13. The device structure of  claim 7 , further comprising a second vertical transistor at a second side of the isolation structure opposite to the first side of the isolation structure. 
     
     
       14. The device structure of  claim 7 , which is a memory structure. 
     
     
       15. The device structure of  claim 14 , wherein the memory structure is a DRAM structure and further comprises a capacitor coupled to the second S/D region. 
     
     
       16. The device structure of  claim 15 , wherein the first S/D region contacts a buried bit line in a second trench in the substrate. 
     
     
       17. The device structure of  claim 16 , wherein two buried bit lines are disposed in parallel in the second trench. 
     
     
       18. The device structure of  claim 16 , wherein the buried bit line comprises a metallic layer and a second doped semiconductor layer having the second conductivity type thereon, and the second doped semiconductor layer contacts the first S/D region. 
     
     
       19. The device structure of  claim 18 , wherein the first S/D region is formed through dopant diffusion from the second doped semiconductor layer.